1. Field of the Invention
The present invention relates to an RFID (Radio Frequency IDentification) tag through which information is exchanged with external equipment in a non-contact manner. The “RFID tag” is called “radio IC tag” in some cases.
2. Description of the Related Art
In recent years, there are proposed various RFID tags through which information is exchanged with external equipment such as a reader/writer in a non-contact manner (see Japanese Patent Application Publication Nos. 2000-311176, 2000-200332 and 2001-351082, for example).
FIG. 1 is a schematic sectional view showing a structure of an ordinary RFID tag.
According to the RFID tag 10 shown in FIG. 1, an antenna pattern 12 is formed on a substrate 11 made of PET, a circuit which carries out radio communication through the antenna pattern 12 is incorporated in an IC chip 13, the IC chip 13 in its bare state is soldered to the antenna pattern 12 with solder 14, a filler 15 is poured into a space under a lower surface of the IC chip 13 and is solidified, thereby forming an RFID tag inlay to which the IC chip 13 is strongly secured, an adhesion layer 16 is placed on the RFID tag inlay and is sealed with a label 17.
In the case of the RFID tag 10 having the structure shown in FIG. 1, however, the following problems are found:
since thermal expansion coefficients of silicon which is a base body of the IC chip 13 and the flexible substrate 11 made of PET are large, long term bonding reliability is poor; and
water or moisture is prone to enter from an end edge of the adhesion layer 16 between the label 17 and the inlay, and the IC chip 13 cannot be applied to a high moisture environment, outside or the like.
Japanese Patent Application Publication No. 2005-275802 discloses an idea to enhance the mounting reliability of the IC chip, but this idea relates to reliability when the chip is mounted, and it is unclear as to the long term stability.
In addition, in the Japanese Patent Application Publication No. 2005-275802, the IC chip is bare, and waterproofing is not provided.
Further, Japanese Patent Application Publication No. 2005-354661 discloses an idea to avoid influence of radio communication on an electronic circuit substrate in a device such as a cellular phone having a radio antenna section, a non-contact communication device which carries out radio communication between the non-contact communication device and external equipment through the radio antenna section, and an electronic circuit substrate, but there is no relation to the long term reliability in respect to influence of temperature, moisture and the like.